Broadband single carrier digital communications receivers often employ both channel equalization and channel decoding to counteract the inter-symbol interference (ISI) caused by time-dispersive channel distortion.
Even so, in severe noise or fading conditions, received information bits may still be in a corrupted state after channel decoding, in which case the receiver may request that a packet is retransmitted, through an Automatic Retransmission Query (ARQ) procedure. In the simplest form of ARQ, the transmitted packet contains error detection bits such that, on detection of an error by the receiver's cyclic redundancy check (CRC), the packet is retransmitted, re-equalized and re-decoded, until the receiver's error detection process identifies that correct decoding has occurred. This retransmission is typically performed up to maximum number of times or a maximum time delay.
When forward error correction (FEC) bits are included in the transmission as well as error detection bits, the retransmission procedure is typically referred to as hybrid-ARQ (HARQ). Hybrid-ARQ can achieve additional performance gain by the soft combining of received coded bits over time (i.e. over multiple retransmissions) in a soft-coded-bit buffer—or HARQ buffer—prior to the decoding stage.
The article by Okuyama et al., “Iterative MMSE Detection and Interference Cancellation for Uplink SC-FDMA MIMO using HARQ”, Proc. of IEEE International Conference on Communications (ICC 2011), Jun. 5-9 2011, Kyoto, Japan, discusses the use of HARQ and interference cancellation. However, the solution of this article is only applicable to chase combining HARQ.